`get_results()` returns Empty Array if no result & `get_set()` tidy up

Previously, a call to get_results() would return NULL if the output was ARRAY and no results were available. I have changed this to return an empty array (as this is the expected response type, is falsely, and prevents type errors when then output it used in a foreach loop.

Also modified get_set() function to pass through reserved SQL words without wrapping as strings ("NULL" != NULL, "NOW()" != NOW()).